1. Technical Field
The invention relates to pneumatic vehicle tires and in particular to a baffle system mounted within the tire to reduce road noise. More particularly, the invention relates to a dynamic baffle system mounted within the tire which becomes effective when the tire is rotating to significantly reduce noise created by the acoustic cavity resonance within the air chamber of the tire by changing the characteristics of the sound waves created within a rotating tire.
2. Background Information
The reduction of noise created by a vehicle tire is a continuing effort for tire designers, whether the noise is generated by the particular tread configuration of the tire or other characteristics thereof. In addition to the various noises caused by the external configuration of the tire and tread, an interior noise is created by the acoustic cavity resonance within the air chamber of a tubeless pneumatic tire. The elimination or reduction of this internal cavity resonance noise is desirable to provide a quieter pneumatic tire, especially for use on passenger vehicles.
The reduction or elimination of this internal noise has been attempted over the years, and various structures, devices and systems have been suggested for achieving this result. One such system is shown is U.S. Pat. No. 4,392,522. This system uses a sound-absorbing insulating material, such as blocks of foam, which are attached to the rim or to the tire interior, or uses foam discs which are bonded to the inner surface of the tire sidewalls. This system is intended to reduce noise by deadening the noise and not by changing the characteristics of the sound waves.
Another prior art system which attempts to reduce or eliminate the noise created by this internal resonance is shown in U.S. Pat. No. 4,909,295. One embodiment of this system uses a separate air valve for inflating a plurality of hollow baffles which are attached to an annular manifold member mounted circumferentially about the rim, wherein the baffles are inflated and extend radially within the annular air chamber of the tire. This system requires additional machining in the rim for an air valve and the additional cost associated therewith. Another embodiment of this prior art system uses rigid plates which are attached to an annular member surrounding the rim, which plates are spring biased to a radially outwardly extending position to form a plurality of internal chamber sections to reduce the noise caused by the acoustic cavity resonance. Although the various embodiments of U.S. Pat. No. 4,909,295 may achieve the desired results, they would be relatively expensive to produce and install, increasing the overall cost of the wheel assembly, and in addition, would increase the difficulty of changing the tire on the rim due to the interference caused by the inflatable baffle members or spring-biased rigid plate members. Furthermore, when a rigid internal plate member is used within the tire, it could cause damage to the tire or baffle if the tire is seriously deflected, such as when hitting a depression or protrusion in the roadway.
U.S. Pat. No. 2,493,731 shows an inner tube for use in a pneumatic tire wherein the tube is subdivided into a plurality of chambers by radial partition walls which are formed integrally with the inner surface of the tube. The chamber walls are formed with slits to permit the flow of air between the internal chambers to cushion shock applied to the tire, and are not concerned with the reduction of noise created by the internal cavity resonance.
U.S. Pat. No. 4,381,026 discloses a wheel assembly which is provided with a plurality of circumferentially spaced paddles mounted on the rim of the wheel, which extend a relatively short distance radially into the air chamber. These paddles direct the air within the air chamber of the tire from the rim toward the tread to transfer heat generated at the tread to the heat sink of the drop center of the rim, and not for noise reduction or suppression.
U.S. Pat. No. 2,780,806 discloses an aircraft tire having internal members which are specially designed reflector units to increase the radar detection of the aircraft during landing when the tire is in a lowered position.
U.S. Pat. No. 1,956,739 discloses a device which is mounted inside the inner tube of a pneumatic tire for cooling the tire by use of a wire bundle which is attached at one end within the tire. The wire bundle distributes fluid contained within the inner tube throughout the interior of the tube to provide cooling for the tire. This wire bundle does not provide any noise reduction by changing the characteristics of the sound waves within the tire.
U.S. Pat. No. 3,047,285 discloses the mounting of a heat sink member within the air chamber of a pneumatic tire, which consists of a plurality of glass fibers attached to the tire rim. These fibers would add a considerably unbalanced weight in the tire and are intended to reduce heat transfer and the build-up of heat within the tire, and are not intended in any manner to reduce tire noise by changing the characteristics of the sound waves within the tire.
U.S. Pat. No. 4,620,580 discloses a belt which wraps around the rim of a tire and extends into a liquid contained within the tire for removing heat to cool the tire. This construction requires liquid inside of the tire, and would not be suitable for pneumatic tires used at high speeds, such as a usual passenger tire. The cooling belt is used in heavy equipment tires that operate at very low speeds, and is not concerned with reducing tire noise by changing the characteristics of the sound waves produced within the pneumatic tire, as is the present invention.
Although several of the prior art devices and systems discussed above are concerned with the reduction of noise generated within the air chamber of a vehicle tire, they all require relatively complicated and expensive devices and structures which increase the cost of the tire and the manufacture thereof, as well as increasing the difficulty of changing the tire after the device or system is in place on the rim or on the interior walls of the tire. These prior art devices also reduce the tire noise by the providing of sound deadening members within the tire, and not by changing the characteristics of the sound waves generated within the tire.
There is no known noise reduction system for vehicle tires of which we are aware which reduces tire noise by the use of flexible non-self-supporting baffles, preferably formed of cloth, which are attached either to the rim of the tire assembly or to the interior of the tire, and which become active only when the tire is rotating, in order to change the characteristics of the sound waves produced within the rotating tire.